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USING GLACIAL DISPERSAL PATTERNS TO UNDERSTAND THE SPATIAL DISTRIBUTION OF SUBGLACIAL QUARRYINGDr

by LaBlanc, Kelly J.

Abstract (Summary)
Quarrying of bedrock beneath a glacier produces coarse-grained sediment, helps maintain bed roughness, and creates rock tools for abrasion. Despite the importance of the process in the formation of glacial landforms and sediments, much remains unknown about its basic mechanics, controlling mechanisms, and rates. Characterizing the variation of quarrying along glacial flowlines is vital in understanding the quarrying process. If the pebble dispersal patterns preserved in glacial sediments do not conform to those predicted by a given model for quarrying, then the ice dynamics and process mechanics that control quarrying are unlikely to be consistent with that model. Three linear functions describing the spatial distribution of quarrying intensity along a glacial flowline were tested using pebble dispersal patterns preserved in the glaciated valleys in the Sawatch Range of Colorado and in the Appalachian Ice Complex of the South Mountain Batholith region of Nova Scotia. The functions represent simple forms of three unique distributions: 1) a case where quarrying is increasing in intensity down a glacial flowline, 2) a case where quarrying is decreasing in intensity down a glacial flowline, and 3) a constant case where quarrying intensity is uniform along the flowline. Iterative computer models combine the quarrying intensity distributions with information on the bedrock distribution and flow history of the study areas to predict pebble dispersal patterns. The modeled dispersal patterns were compared to observed patterns statistically to identify the best fit. The case where quarrying intensity is distally increasing was found to best predict observed pebble dispersal patterns. Modeling indicated that dispersal patterns were probably created during the advance phase with only minor modification during the retreat phase. Dispersal patterns in the South Mountain Batholith area are mostly the result of the last phase of glaciation with little inheritance from previous phases. The agreement between the two study areas suggests that the controls on quarrying or that quarrying mechanisms are independent of the size of the ice mass. The increasing intensity of quarrying in the marginal area is likely due to increased frequency and magnitude of water pressure changes in subglacial cavities.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:subglacial erosion quarrying glacial dispersal sawatch range nova scotia

ISBN:

Date of Publication:01/01/2007

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